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Radio Astronomy: Observing the Invisible Universe

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Course Overview

It’s easy to imagine the first modern humans staring up at the heavens in wonder, their eyes and minds dazzled by a beautiful band of light splashed across the night sky, the ever-changing moon so large and bright, and pinpoints of light in every direction. For a few hundred thousand years, our eyes were our primary astronomical tool, and we used them well. We catalogued and analyzed what we saw, filled in the gaps with powerful stories, applied what we knew of mathematics, and then invented complex tools of stone, metal, and glass to expand our knowledge. Everything we knew about the universe was based on light, that small part of the electromagnetic spectrum detectable by human eyes.

Then one day in the 1930s, a young engineer named Karl Jansky was assigned a task at Bell Labs: What were the sources of radio static that could interrupt transatlantic radio communications? After several years of work, he identified one source as radio waves coming from thunderstorms near and far… and another, from something at the center of the Milky Way. For the very first time, we had detected radiation below the visible part of the spectrum emanating from an astronomical object. For years, astronomers had been frustrated by interstellar dust that blocked their view and limited their

Radio Astronomy: Observing the Invisible Universe takes you on a thrilling journey through the universe with stunning visuals and animations to explain the science of radio astronomy and its astounding discoveries. Your guide is Felix J. Lockman, Ph.D., of the Green Bank Observatory, an active radio astronomer whose great passion for his work is absolutely contagious. As Dr. Lockman explains, radio astronomy is not simply a conglomeration of theories with no practical application to our lives today. While radio astronomy has the potential to one day answer the question of extraterrestrial intelligence, it also allows us to more accurately tell time right here on Earth, study terrestrial plate tectonics, and even get smartphone directions to that great new restaurant.

All about That Hydrogen

Some of radio astronomy’s myriad discoveries can be traced to the structure of the hydrogen atom. In hydrogen, one electron is essentially in orbit around one proton and both have a property called “spin,” either up or down. The parallel spin “wants” to decay into antiparallel spin—much like two magnets “wanting” to be aligned north to south, or antiparallel. In jumping position from parallel to antiparallel, a photon of radiation is emitted.

This process is certainly not unique to hydrogen. What is unique is that at the dawn of radio astronomy, a scientist predicted hydrogen would emit this radiation at detectable radio wavelengths, and this prediction offered astronomers a new tool for studying the universe. Three teams of scientists from around the world worked to discover the signal, and there it was, exactly as predicted: with a frequency of 1420 MHz, a wavelength of 21 cm.

For more than a decade, hydrogen at 21 cm wavelength remained the only spectral line which radio astronomers could use for their research. Later, signals from other elements and even molecules were identified. Over time, as both theory and technology improved, radio astronomers made discoveries that completely changed our understanding of the universe. Just a very few of these discoveries include:

Jupiter’s radiation belts;

Galactic non-thermal radiation, now called synchrotron emission;

The birth rate of stars in the Milky Way and the galaxy’s rotational speed;

Sagittarius A, the black hole at the center of the Milky Way;

Dark matter;

Neutron stars, pulsars, and binary pulsar systems;

Gravitational radiation, as predicted by Einstein;

Cosmic background radiation, confirming the big bang theory;

Radio galaxies, quasars, and active galactic nuclei;

Giant molecular clouds, the birthplaces of stars and planets; and

Complex organic molecules in interstellar space.

Radio Telescopes, “Seeing” the Invisible

While you might have an optical telescope in your backyard, you will likely never have a radio telescope. Radio telescopes are large—over 100 meters in diameter and beyond—because radio waves contain such a small amount of energy. For example, the signal from your cell phone measured one kilometer away is five million billion times stronger than the radio signals received from a bright quasar! Although each radio telescope is designed for a specific use and often looks very different from others, they are all based on the same physical principles. Each collects, focuses, amplifies, and analyzes radio waves. In Radio Astronomy: Observing the Invisible Universe, Dr. Lockman takes you on an exciting virtual tour of radio telescopes. From the first handmade telescope built by radio astronomy pioneer Grote Reber to those on the drawing board for tomorrow, you’re right there with the scientists:

The Green Bank Telescope, West Virginia, where Dr. Lockman does his research. At 17 million pounds and with more than 2,000 surface panels that can be repositioned in real time, this telescope is one of the largest moveable, land-based objects ever built.

The Very Large Array (VLA), New Mexico. With its 27 radio antennas in a Y-shaped configuration, the data can be multiplied to form interference patterns, giving scientists a deeper and clearer look at galaxies than ever before.

The Atacama Large Millimeter/submillimeter Array (ALMA), Chile. With an array of 66 radio antennas located high above much of the earth’s atmosphere, ALMA has revealed new stars and planetary systems in the making.

The Very-Long-Baseline Array (VLBA), with multiple locations. The VLBA includes telescopes located thousands of miles apart, all functioning together as one single radio telescope the size of the Earth, allowing scientists to peer deep into the centers of galaxies.

The Biggest Questions

Perhaps the most astounding of all radio astronomy discoveries is this: The dominant molecular structures in interstellar space are based on carbon. That is not what scientists had expected.

We have always labeled these molecules “organic” because life on Earth is carbon based. Now we know that the chemistry of the entire Milky Way is organic, not just our home planet, and it is likely that any extraterrestrial galactic life would be related to us, at least on the molecular level. Will we find other organic lifeforms out there? Radio astronomers don’t know. But they’re working on it, along with the study of many other objects and processes not yet understood. Dr. Lockman’s current research addresses hydrogen clouds in the Andromeda galaxy, the nearest major galaxy to the Milky Way. Other radio astronomers are working to answer myriad questions about dark matter, fast radio bursts, and much more.

If the history of radio astronomy is any predictor, discoveries in these new research areas will lead to new questions, new technologies, more discoveries, and more questions. As Radio Astronomy: Observing the Invisible Universe shows, the field is on the cutting edge of knowledge itself. “Astronomy, by looking outward, leads us to questions that reflect upon ourselves in very deep ways,” Dr. Lockman says. “Astronomical discoveries have changed the way we think.”

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24 lectures

| Average 31 minutes each

1

Radio Astronomy and the Invisible Universe

Even on the clearest, darkest night you cannot see more than five percent of the light from our home galaxy, the Milky Way, because of the blockage of light by dust. Fortunately, the 20th century brought us radio astronomy, the study of radio waves that travel through the dust, opening our eyes" to a universe we had never imagined." x

2

Thermal Radio Emission: The Planets

Take a tour of our neighboring planets via their radio emissions and learn how scientists infer their temperatures and energy sources. You'll be shocked by the difference between their images in reflected sunlight-the images we're familiar with-and their appearance when we "see" the radio energy they emit on their own. x

3

The Birth of Radio Astronomy

When young engineer Karl Jansky was tasked to find natural radio sources that could interfere with commercial transatlantic radio communications, radio astronomy was born. His work, and that of backyard astronomer Grote Reber, led to the discovery of synchrotron radiation. But it would be decades before scientists understood what these earliest radio astronomers had detected-cosmic rays and magnetic fields. x

4

The Discovery of Interstellar Hydrogen

Not long after the birth of radio astronomy, a Dutch student used what was then known about the physics of atoms to determine that if hydrogen existed in interstellar space, it would produce a specific spectral line at radio wavelengths. In 1951, the line was detected at 21 cm, exactly as predicted. At that moment, our understanding of the universe forever changed. x

5

Radio Telescopes and How They Work

Radio telescopes are so large because radio waves contain such a small amount of energy. For example, the signal from a standard cell phone measured one kilometer away is five million billion times stronger than the radio signals received from a bright quasar. Learn how each of these fascinating instruments is designed to meet a specific scientific goal-accounting for their wide variation in form and size. x

6

Mapping the Hydrogen Sky

Before there were stars and planets, before there were galaxies, there was hydrogen-and we still have more hydrogen today than any other element. Understanding the quantum physics of this simplest atomic structure, and using the Doppler shift and models of differential rotation in the Milky Way, astronomers have made myriad astounding discoveries about the universe. It all starts with hydrogen. x

7

Tour of the Green Bank Observatory

The Green Bank Observatory is located within the 13,000-acre National Radio Quiet Zone straddling the border of Virginia and West Virginia. Come tour this fascinating facility where astronomers discovered radiation belts around Jupiter, the black hole at the center of our galaxy, and the first known interstellar organic molecule, and began the search for extra-terrestrial life. x

8

Tour of the Green Bank Telescope

At 17 million pounds, and with more than 2,000 surface panels that can be repositioned in real time, this telescope is one of the largest moveable, land-based objects ever built. The dish could contain two side-by-side football fields, but when its panels are brought into focus, the surface has errors no larger than the thickness of a business card. Welcome to this rare insider's view. x

9

Hydrogen and the Structure of Galaxies

Using the laws of physics and electromagnetic radiation, astronomers can weigh" a galaxy by studying the distribution of its rotating hydrogen. But when they do this, it soon becomes clear something is very wrong: A huge proportion of the galaxy's mass has simply gone missing. Welcome to the topsy-turvy world of dark matter-which we now believe accounts for a whopping 90 percent of our own Milky Way." x

10

Pulsars: Clocks in Space

In the mid-1960s, astronomers discovered signals with predictable periodicity but no known source. In case these signals indicated extraterrestrial life, they were initially labeled LGM, Little Green Men. But research revealed the source of the pulsing radiation to be neutron stars. Learn how a star with a diameter of only a few kilometers and a mass similar to that of our Sun can spin around hundreds of times per second. x

11

Pulsars and Gravity

A pulsar's spin begins with its birth in a supernova and can be altered by transfer of mass from a companion star. Learn how pulsars, these precise interstellar clocks, are used to confirm Einstein's prediction of gravitational waves by observations of a double-neutron-star system, and how we pull the pulsar signal out of the noise. x

12

Pulsars and the 300-Foot Telescope

Humans constantly use radio transmission these days, for everything from military communications to garage-door openers. How can scientists determine which signals come from Earth and which come from space? Learn how the 300-foot telescope, located in two radio quiet zones, was built quickly and cheaply. It ended up studying pulsars and hydrogen in distant galaxies, and made the case for dark matter. x

13

The Big Bang: The Oldest Radio Waves

Learn about techniques to separate signals originating in receivers from signals originating from outer space. Using a unique antenna located in New Jersey, we'll see how two radio astronomers with curiosity, persistence, and some manual labor, detected the faint radio signals from the big bang, the oldest electromagnetic radiation that can be detected. It tells us of conditions when the universe was young. x

14

H II Regions and the Birth of Stars

Have you ever looked up to Orion on a dark winter's night and noticed a fuzzy patch near the center of the constellation? You're looking at the Orion nebula, a nursery" where stars are born every year. Learn why ionization occurs in these H II regions and how this hot plasma produces some of the most beautiful objects in the sky." x

15

Supernovas and the Death of Stars

Chances are you would agree with astronomers that gravity is the single most important force or event shaping the world as you know it. But the second most important? That would be supernovas, and nothing you know would be here without them. Learn how super-massive stars can explode at the end of their lives, releasing energy that outshines 10 billion Suns. x

16

Radio Stars and Early Interferometers

When radio astronomers discovered a sky full of small radio sources of unknown origin, they built telescopes using multiple antennas to try to understand them. Learn how and why interferometers were developed and how they have helped astronomers study quasars-those massively bright, star-like objects that scientists now know only occur in galaxies whose gas is falling into a supermassive black hole. x

17

Radio Source Counts

Radio source counts have led to great discoveries about the universe, even though each individual radio source isn't fully understood. Between massive black holes and starbursts, scientists relying in part on astronomical surveys now believe galaxies can have different evolutionary tracks and histories. And the universe itself? It seems to be not only evolving, but evolving through stages. x

18

Active Galactic Nuclei and the VLA

The need for a new generation of radio interferometers to untangle extragalactic radio sources led to the development of the Very Large Array (VLA) in New Mexico. With its twenty-seven radio antennas in a Y-shaped configuration, it gives both high sensitivity and high angular resolution. The VLA provided a deeper and clearer look at galaxies than ever before, and the results were astonishing. x

19

A Telescope as Big as the Earth

Learn how astronomers use very-long-baseline interferometry (VLBI) with telescopes thousands of miles apart to essentially create a radio telescope as big as the Earth. With VLBI, scientists not only look deep into galactic centers, study cosmic radio sources, and weigh black holes, but also more accurately tell time, study plate tectonics, and more-right here on planet Earth. x

20

Galaxies and Their Gas

In visible light, scientists had described galaxies as island universes." But since the advent of radio astronomy, we've seen galaxies connected by streams of neutral hydrogen, interacting with and ripping the gasses from each other. Now astronomers have come to understand that these strong environmental interactions are not a secondary feature-they are key to a galaxy's basic structure and appearance." x

21

Interstellar Molecular Clouds

In the late 1960s, interstellar ammonia and water vapor were detected. Soon came formaldehyde, carbon monoxide, and the discovery of giant molecular clouds where we now know stars and planets are formed. With improvements in radio astronomy technology, today's scientists can watch the process of star formation in other systems. The initial results are stunning. x

22

Star Formation and ALMA

With an array of 66 radio antennas located in the high Chilean desert above much of the earth's atmosphere, the Atacama Large Millimeter/submillimeter Array (ALMA) is a radio telescope tuned to the higher frequencies of radio waves. Designed to examine some of the most distant and ancient galaxies ever seen, ALMA has not only revealed new stars in the making, but planetary systems as well. x

23

Interstellar Chemistry and Life

Interstellar clouds favor formation of carbon-based molecules over any other kind-not at all what statistical models predicted. In fact, interstellar clouds contain a profusion of chemicals similar to those that occur naturally on Earth. If planets are formed in this rich soup of organic molecules, is it possible life does not have to start from scratch on each planet? x

24

The Future of Radio Astronomy

Learn about the newest radio telescopes and the exhilarating questions they plan to address: Did life begin in space? What is dark matter? And a new question that has just arisen in the past few years: What are fast radio bursts? No matter how powerful these new telescopes are, radio astronomers will continue pushing the limits to tell us more and more about the universe that is our home. x

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About Your Professor

Felix J. Lockman, Ph.D.

Principal Scientist at the Green Bank Observatory

Felix J. Lockman, Ph.D., is the Green Bank Telescope Principal Scientist at the Green Bank Observatory, a facility of the National Science Foundation. He did his undergraduate work at Drexel University and received his Ph.D. from the University of Massachusetts Amherst. Dr. Lockman’s area of research is the structure and evolution of the Milky Way and nearby galaxies, with a special emphasis on radio observations of neutral...

Reviews

Radio Astronomy: Observing the Invisible Universe is rated
4.8 out of
5 by
83.

Rated 5 out of
5 by
3C296 from
Exceptional courseCourse was very well done and highly informative. I highly recommend it. The course was well laid out and engaging. Great intro to radio astronomy!

Date published: 2019-01-12

Rated 5 out of
5 by
use your own brain from
More insightLearning amazing new things. The more I learn, the more my ignorance shows.
Am 78 years old and still love to learn. No other courses I have taken have covered this material.

Date published: 2018-12-10

Rated 5 out of
5 by
Raymond from
Great learning experienceI started watching this course a second time I love it!

Date published: 2018-10-21

Rated 5 out of
5 by
psneeley from
A very comprehensive, satisfying course!A comprehensive, in-depth, look at Radio Astronomy from a great teacher. I learned so much, and it was fun! No math to speak of, but good graphics, and solid real-world experience by a working scientist in the field. I just finished my second time through the lectures and I am sure I will return a third time – there are concepts here that you are just not going to learn in a general Astronomy course (although The Great Courses’ 96-lecture ‘Astronomy’ course, taught by Alex Filippenko is a wonderful also, there just isn’t time there to focus in any depth on Radio Astronomy). Thanks Dr. Lockman!

Date published: 2018-09-22

Rated 5 out of
5 by
Great Courses from
Well done!For the many of us who have an interest in the subject, but know very little about it, this is a very worthwhile course. Prof. Lockman makes the more complex aspects of radio astronomy very easy to understand, and he has a pleasant presentation style. I should have gotten this course long ago.

Date published: 2018-08-13

Rated 4 out of
5 by
CivilE from
Great explanation of radio astronomyGreat explanation of radio astronomy and how it has expanded our understanding of the universe. Professor Lockman has great enthusiasm for the subject and provides an informative and entertaining review of the subject.

Date published: 2018-08-04

Rated 5 out of
5 by
Prasad Ganti from
Really a great courseDr. Lockman is an excellent teacher. The course material is well selected. Adds lot of information on astronomy in general and radio astronomy in particular. The tour of Green Bank observatory is an added bonus.

Date published: 2018-07-28

Rated 4 out of
5 by
Viewer from
Easy to understandI've only watched the first 3 sections. The instructor is very knowledgable and explains things in a way that is easy to understand, with diagrams, etc.